The lexicon of carpentry-speak is littered with registered trade names. Through widespread use, these brand names are now considered generic terms. For example, a circular saw is often referred to as a Skilsaw, and a reciprocating saw is called a Sawzall. Ever heard anyone ask for a pair of self-locking pliers? Of course not, they ask for Vise-Grips.
Well, the same recognition has been bestowed upon an ingeniously simple layout square known to all carpenters as a Speed Square. Invented in 1925 by carpenter Albert J. Swanson, the triangular-shaped square was originally developed to provide a faster, more accurate way to mark roof rafters. Today, however, the Speed Square can do much more, and has become an indispensable part of every carpenter's tool collection. Here's a brief look at just some of the ways to use this super-versatile tool:
The most common use of the Speed Square is to mark square lines at precisely 90 degrees to the board's edge. This job is greatly simplified by the fact that the tool has as a lipped fence running along one edge, which allows you to quickly—and accurately—hold the tool against a board's edge while marking lines along the square's side.
Being able to quickly draw square lines is particularly useful for jobs that require repetitive, accurate markings, such as locating studs on wall plates, positioning floor joists on decks and laying out stair stringers for staircases. And when building cabinets and other "boxes," the Speed Square is handy for aligning two pieces at a right angle during assembly.
Because the Speed Square is an isosceles right triangle, its long, diagonal edge is machined precisely at 45 degrees to the tool's fence. There are no adjustments to make or moving parts to get knocked out of whack. Just press the fence tight against the board and mark along the square's diagonal edge to draw a precise 45-degree line.
Of course, you can mark 45-degree lines with a combination square, but its handle (fence) is only about 3 inches long, which can lead to imprecise markings. The fence of the smallest model Speed Square is over 7 inches long, which provides superior support and ensures very accurate markings.
Reading, laying out and marking angles typically requires a protractor or a sliding-bevel square, or both. However, the Speed Square has degree graduations stamped along its diagonal edge, so reading and marking angles is easy.
At the corner of the square, near one end of the fence, is a pivot point. Along the diagonal edge are lines, each representing one degree, ranging from zero to 90. To mark a particular angle, let's say, 35 degrees, simply hold the pivot point against the board, then adjust the square until the 35-degree graduation aligns with the edge of the board. Now draw a line along the square opposite the diagonal edge. Note that the Speed Square has separate graduations for marking both common roof rafters and hip and valley roof rafters. The square can accommodate roof rises (angles) ranging from 1 inch of rise in 12 inches of run, to 30 inches of rise in 12 inches of run.
One of the most useful, but often overlooked, features of the Speed Square is its line-scribing capabilities. There are two rows of notches machined into one of the square's slots. The notches in each row are precisely spaced ½ inch apart, but the rows are staggered ¼ inch in alignment, effectively providing a notch every ¼ inch.
To mark a parallel line, press the square's fence tight against the board's edge, then place the pencil tip into the appropriate notch. Now slide the square along the board, making sure to keep its fence against the edge and the pencil in the notch. The result will be a line that's perfectly parallel with the board's edge. Use this scribing technique to mark cut lines on plywood or layout lines on framing lumber.
Perhaps the most practical—and practiced—use of the Speed Square is not as a square at all, but as a straightedge guide for a portable circular saw. In fact, there's no better, quicker way to crosscut lumber than with a Speed Square: Place the square flat down on the board, with its fence tight against the board's edge. Slide the saw shoe up against the square, and make the cut. Because the Speed Square is thicker than a framing square or combination square, the saw is much less likely to ride up on top of the square. That increases both accuracy and safety.
You may need to make a few test cuts before feeling comfortable, but before long you'll be able to make perfectly square crosscuts. Just be sure to hold the square securely in place, and keep the saw shoe pressed against the square throughout the cut.
Most carpenters place the square on the outer edge of the board (the edge farthest away), so they can pull the square and the board toward themselves, while pushing the saw away in the opposite direction. If you feel more comfortable holding the square against the near edge, that's fine, just be sure to clamp the board in place to prevent it from moving. —Joseph Truini